Conventionally, for various purposes including security, capturing or search of photos or videos, organization thereof, and the like, techniques for detecting a detection target such as a face or a person from data such as an image, a sound, or a sensor signal, have been studied. In particular, in recent years, techniques for detecting a detection target from an image using a classifier generated by machine learning, have been extensively studied. For example, a classifier for determining whether an image contains a person is generated, using a feature parameter(s) extracted from each of a large number of images for learning that contain a person and a large number of images for learning that do not contain the person, to perform machine learning of a decision boundary that partitions a feature parameter(s) space into a space where feature parameters of the person are distributed and a remaining space. When the feature parameter(s) extracted from the image is input, the classifier determines whether the image contains the person, depending on which side of the decision boundary the feature parameter(s) is located in the feature parameter(s) space.
However, images containing a person and images not containing the person have diversity, and it is generally difficult to find a decision boundary that can completely separate these images. In particular, for example, a feature parameter(s) extracted from an image containing something similar to a person, like a jacket hung on a hanger or the like, is highly likely to be located on a space side of a decision boundary where feature parameters of the person are distributed, which may lead to an erroneous determination that the image contains the person.
Accordingly, for example, Patent Literature 1 has proposed an object detection device for causing a classifier to learn in accordance with characteristics of an installation environment of the device. The object detection device causes the classifier to learn using images from a monitoring camera upon installation of the monitoring camera.